Although hypotension during dobutamine stress echocardiography has been reported, the mechanism of this response is still controversial. In two patients, a 72-year-old woman and 64-year-old man, with exercise-induced ST-T change, continuous-wave Doppler examination of the left ventricular cavity was performed at baseline and peak dobutamine infusion. No echocardiographic abnormalities at rest or angiographic coronary lesions were observed in either patient. The intracavitary pressure gradient at peak dosage of dobutamine for both patients was 121 mm Hg and 100 mm Hg, and was reproducibly confirmed by cardiac catheterization. During dobutamine infusion, echocardiography or left ventriculography revealed that papillary muscle motion was dramatically augmented by dobutamine and mid-left ventricular obstruction was produced at the systolic phase. Although blood pressure response improved following beta-blocker treatment, intracavitary pressure gradient during dobutamine infusion remained the same. A hypotensive response during dobutamine stress echocardiography may be produced by the development of dynamic intraventricular obstruction and a vasodepression reflex. The exercise-induced electrocardiographic changes may have been related to the systolic pressure augmentation in the mid-to-apical left ventricular cavity.